“Emerging infections” are those that appear suddenly or are rapidly increasing in incidence or geographic range (e.g., HIV/AIDS, Ebola, SARS, Middle East Respiratory Syndrome [MERS], H5N1 avian influenza, pandemic influenza, Zika). Most are pathogens from other species that acquire opportunities to come in contact with humans and spread (often as a result of such factors as changes in ecology and land use, increasing urbanization, and human movement). A pandemic is an epidemic that spreads to cover a broad geographic range. Despite progress in identifying the underlying factors (or “drivers”) and improvements in early warning, no emerging infection or pandemic to date has been correctly predicted before its appearance in humans. In two of the most recent epidemics, Ebola in West Africa and Zika in the Americas, the first outbreaks were initially discounted. Before the recent reports of neurological effects, Zika, a mosquito-borne virus that came to Brazil from the Pacific Islands only two years ago and had been circulating in Africa far longer, was considered a mild disease and little cause for concern. By contrast, Ebola's lethality has been legendary since its first identification in 1976, but an epidemic with over 11,000 fatalities seemed inconceivable. Such surprises demonstrate that population density, and host social and biological factors, likely play as important a role in the development of pandemics as characteristics of the pathogen, and should serve to warn against complacency. Our current approach is reactive. Although we have the capability to develop more effective systems to anticipate and prevent emerging infections and pandemics, much more needs to be done. Many effective public health measures, such as immunization and mosquito control, often become victims of their own success and are not sustained. As urbanization increases worldwide, effective and sustainable early warning and response remain ever more essential.
1. Define and distinguish an emerging infection and a pandemic
2. Assess probable future pandemic risks and how they might be prevented